Such a method is known from the Applicant's European Patent Application 201,952 filed on 10 Apr. 1986. In accordance with this prior document a given amount of encapsulant is introduced into the recess of the card by means of an automatic metering device, after which the cover section is fitted and the card is reversed. The encapsulant then flows onto the integrated-circuit chip but remains in the recess because this is closed by the cover section. This method improves the resistance to repeated bending of the card but it does not guarantee a reproducible encapsulation of the circuit. However, for an optimum reliability of the card it is desirable that the integrated circuit and its connection wires are wholly encapsulated.
Techniques for the complete encapsulation of a chip card are known but they all exhibit comparatively large drawbacks, in particular a fairly large number of process steps.
European Patent Application 075,351 filed in the name of the Applicant and N. V. Philips on 7 Sep. 1982 teaches to arrange an integrated circuit on the bottom of a cavity in a base, which integrated circuit is electrically connected to metallised tracks on the two surfaces of the auxiliary support. Subsequently, the cavity is filed with an insulating wax which, once it has solidified, holds the integrated circuit and the connection wires in position. For this purpose a frame is arranged on the support 11 around the cavity. The assembly thus obtained consequently does not exhibit a flat surface because the frame constitutes a thicker portion, the method not being applicable in any case to a card in accordance with the cited document 201,952.
Moreover, European Patent 107,061 (N. V. Philips) describes a card having a card base formed with a cavity open to both surfaces of the card. The circuit support (4) is covered with a foil (6) at its lower surface, the circuit (5) is arranged on the foil (6) through an opening (10) in the circuit support, and subsequently the connection wires are arranged between the circuit and the circuit support. After this, an annular sealing element (8) is arranged on the circuit support so as to surround the circuit and the connection wires, and subsequently a filling substance (9) is applied in order to embed the circuit and the wires, after which the foil (6) is removed. This method has the drawback that as a result of filling with a resin it is not possible to obtain a flat surface owing to the precision attainable with automatic metering devices and owing to the capillarity effect. Therefore, a finishing operation is necessary to give the card a flat surface. This is a drawback common to all the techniques in which the cavities are filled via the back. Thus, the cards manufactured by Messrs. Schlumberger employ a card base having a hole accommodating a polyester printed circuit MCTS carrying an integrated circuit, filling with an epoxy resin being effected via the back, after which the surplus resin is subjected to a finishing operation. It is to be noted also that, as a result of the materials used, this method has the drawback that the device is visible, which poses a problem with respect to the appearance of the product.
Another total encapsulation technology is used by Siemens. A chip is interconnected to a film by gold pads and is accommodated in a cavity in an inner layer of a card base comprising a plurality of PVC layers. This technique, which requires a plurality of layers to be stacked, is expensive.
It is an object of the present invention to solve the problem of the production costs of "total encapsulation" cards.
Until now the technology corresponding to European Patent 201,952 has been used, in which the connection wires are encapsulated only partly or not at all, the product being designed to withstand bending tests. For this, reference is made to, for example, French Patent Application FR 2,617,668 (RTC-Compelec). The card base in accordance with this technology can be realised at low cost (by moulding) and the embedding process as described in European Patent 201,952 can be automated very easily.
A known total encapsulation technology suitable for a card having a recess for a cover section is to apply and to polymerise a drop of epoxy resin on an integrated device so as to encapsulate the assembly comprising the device and the connection wires (cf. French Patent Application published under number FR 2,583,574 filed by La Societe Eurotechnique on 14 Jun. 1985). In practice, a mechanical finishing operation is necessary because the applied drop forms a dome of a height H, which height must be reduced in practice in order to achieve that the thickness of the combination of printed circuit, chip and encapsulation does not exceed the limits imposed by the dimensions specified for a chip card (nominal thickness 0.8 mm). In practice, this height reduction is obtained by machining the dome so as to flatten it substantially down to the level of the connection wires.